I had this problem in the rented condo where I used to live, and I was the one doing the flushing!

Perhaps others will chime in, but since I bought a new toilet for my recently purchased house (an American Standard Cadet 3) I notice that I get more flushes out of it before it overflows on the rare occurance that it blocks. The old one in the condo would overflow with the first flush after the blocked flush. I get about two/three out of the Cadet 3, by which time I stop and get the plunger. But it has not spilled on the floor yet, unlike the one in the Condo. And if it did there would be less water on the floor....hopefully.

So what I am saying is that I have not seen a toilet that will prevent overflow but the newer, smaller capacity toilets (I would guess of any brand) will take a little bit more flushing to overflow when blocked than the old larger tank models.

Alternatively you could install a toilet that blocks less easily (again my Cadet 3 is good) or change his toilet paper. I have awful problems with Charmin, even on my new toilet, and any brand that feels cottony or soft is a bad idea. Thin, 1000 sheet rolls are the best.

You could also try a Floodstop valve but this could cause you more trouble than it is worth through false alarms (I removed mine because of them). This electronic valve will shut-off the water to the toilet when it senses a wet floor. So if he is flushing an already overflowed toilet, this will stop him. But think carefully before taking this route. It will not stop the toilet overflowing in the first place and because they are prone to false alarms you may need to teach him how to reset it (and my grandmother cannot even operate a microwave).

You need to try to determine if it is overflowing because it gets filled with shit and paper and can't be flushed, or if the pipes are clogged. If the toilet is used multiple times before it is flushed, that could be a problem. If the pipes are partially clogged, then it could happen with any toilet. To ensure the toilet is flushed after each use, you may be able to install an automatic valve. Most use IR and detect when you leave to flush the toilet. I'm pretty confident you've seen this type of valve in various commercial installations. It would depend somewhat on what the supply line to the toilet is which kind and even if this is feasible.

I don't think you can idiot-proof a toilet. If it gets clogged, then it will overflow.

I worked in an old folk's home, and we had to deal with overflows on a daily basis. Best thing to do is to contain the sh!t water to the bathroom by caulking the base of the toilet all the way around, as well as caulking the entire perimeter of the floor.

FWIW, I visited Aqua One a years ago when they were developing their H2Orb product specifically designed to stop toilet overflows. At that time they were saying they were getting much interest for hospital and hotel installations. Searching around Google today I don't see much news about them - wonder what happened. (probably the water level sensors were a problem with feces and TP).

There have been a couple of good suggestions offered. It is true that some toilet paper tends to cause clogs more than others. I would concur with Verdeboy about caulking completely around the base so you can at least contain the overflow, but since you have had overflows already, I'd pull the toilet and clean and disinfect first. A new low flow ADA height toilet such as the Toto Drake might be a good option. The large trap way in the Drake is almost clog proof, the low flow means it would take more flushed to overflow, and the ADA height would not only give more capacity to the toilet bowl, but is much more comfortable to use than the standard height. The ADA height is about the same as a dining room chair. Combine these things with frequent check ups, and you may have the answer. You will for sure have a superior toilet.

If the problem is user related and not anything to do w/ the plumbing itself - the only option to guarantee no overflow is a lowboy toilet. One where the fill line on the tank is level with just below the rim of the bowl. That way if the bowl is full, a second flush won't do anything because the float won't drop down due to water in the tank having nowhere to go.

Of course the lowboy toilets don't have awesome flushes and a new toilet from Toto or any toilet w/ a computer designed "GLAZED" trap of 2 1/8" will reduce most chances of clogged flushes. You want the trap to not pinch, you want it to stay round all the way out of the toilet. Older designs that took 5 gallons in the old days worked fine, but they reduced the volume of water and the weight of the push to get stuff through those old traps. That's why larger more open traps pioneered mostly by Toto has removed the stigma of low water consumption toilets.